Color setting apparatuses for sensing the color of a tooth surface are known, and an example of is described in DE-OS 195 34 517. This publication discloses a light source for emitting light along three paths to irradiate a tooth surface, and three corresponding sensors each for sensing the respective brightness of one of three base colors. It is taught that evaluation or analysis of the sensed results should lead to the least possible color deviation from the available tooth colors.
It is further conventionally known that reflected light or reflections distort or falsely influence the evaluation or analysis results. The arrangement of the light sources at various angles and emission of light therefrom at various spectra permits some compensation of the tendency toward reflection.
It has long been known that, due to the reduced or modest peak-to-valley thickness of the tooth surfaces, reflections distort the color analysis. In order to maintain the least possible degree of reflection, it is known to apply titanium oxide powder on the tooth surface as a contrast powder. However, depending upon the strength or thickness of the applied layer, a distortion of the color analysis is possible.
In order to avoid the disadvantages of contrast powder, the use of a fluorescing color has been suggested (compare DE-OS 40 37 007) whereby the fluorescing color absorbs the green color and emits gold or red. However, a decided disadvantage of such a fluorescing color lies in the fact that the color is distorted so that a compensation therefor must be undertaken in the event that the light shift is to be captured or sensed. Also, it is difficult to apply the fluorescing color exactly in a uniform strength or thickness, as a result of which this approach has not heretofore found widespread acceptance.
In connection with the evaluation of the tooth surface structure, it is desirable, in contrast to the evaluation of the tooth surface color, to capture or sense shadows which reveal or indicate the structure. In this context, as well, the application of a contrast powder or fluorescing color leads to distortion as the shadowing or the like is thereby reduced or eliminated.
It has further already been suggested to use a rotatable polarization filter which, in accordance with the wishes of the user, can be configured to permit the polarized light reflectance to be passed therethrough or to be reduced in an infinitely variable manner. This approach, indeed, permits the comparison of a tooth surface with and without reflection. However, the analysis of the sensed result is strongly dependent upon the angle at which the light source irradiates the tooth surface. Those areas of the tooth surface remote from the light source are frequently darkened or cast in shadow in an arrangement in which the light source is disposed to the side of the tooth surface and, consequently, such areas of the tooth surface cannot readily be recognized or sensed.